1. Field of the Invention
The field of the invention is the removal of particles from a flowing fluid.
2. Description of the Related Prior Art
There are a number of applications in which it is desirable to recover certain solids or particles from a flowing liquid because those solids have economic value. For example, it may be desirable to recover seeds, pulp or other matter from flowing juices or other liquid food. Particles may need to be removed from flowing crude oil, gasoline or similar liquid. Additional applications may be found in the paper making and brewing industries. Though the preferred embodiment of the present invention is used in cheese making, the invention is not limited to that industry.
It has long been known to remove particles from a flowing liquid with a mesh strainer set crosswise in the flow of liquid. As the liquid flows through it, particles are deposited on the strainer. Among the disadvantages of this system is the fact that it must be shut down to allow the strainer to be removed and cleaned. It has further disadvantages in applications where it is desired to save and reuse the recovered particles and where maintaining sanitary conditions is crucial. For example, in a food system, the collection of the particles on the screen and manual removal of them may fail to meet the required sanitary standards, and the quality of the retrieved particles sometimes degrades. Further, this apparatus does not lend itself to "cleaning in place" ("CIP"). This refers to food processing systems which can be cleaned by pumping cleaning fluids through it without disassembly.
In addition to such cross-flow strainers, in-line strainers have been developed, primarily to purify liquid as opposed to recover solids. In typical applications, especially in the food industry, such a strainer is a hollow perforated cylinder which is mounted longitudinally within the conduit carrying the particle laden liquid. Often this strainer is covered with a wire mesh overlay. As the liquid flows through the conduit and along the strainer, particles adhere to the cylinder or the mesh overlay. This type of strainer is less susceptible to blowouts than cross-flow strainers and therefore can handle a higher volume of flowing liquid. However, as with the earlier system, it relies on clogging a strainer to purify a liquid, and the line must be shut down and disassembled in order to be cleaned, with the attendant economic and sanitation disadvantages. As with the earlier system, it is ill-suited for economical recovery of particles of marginal value.
In the making of cheese, there has been a particular need for an effective and efficient system to recover and use curd particles (called "fines") found in the whey which is removed during the processing of cheese. Ideally, such a system would meet the following objectives:
(a) continuous in-line recovery of fines from the flowing whey; PA1 (b) simplicity and low cost in relation to the value of the recovered fines; PA1 (c) meeting the sanitary and other requirements of the food industry and the U.S. Food and Drug Administration, the U.S. Department of Agriculture and other regulatory bodies;; PA1 (d) compatibility with C.I.P.; PA1 (e) minimization of degradation or contamination of the quality of the recovered curds.
To make cheese, a mixture of milk, renin, a micro organism and other materials are processed in a vat. The result of each batch consists of chunky curds and more liquid whey. The batch is moved to and allowed to stand in a shallow vat (called a finishing table or a drain table) with a screened drain. The whey flows out of the drain, leaving the vat filled with curds, which eventually becomes the cheese. However, the whey carries "fines" with it.
One method for recovering the fines is to pump the whey into a whey storage tank in which the fines are separated from the whey in a settling process. The long duration of this process results in acid activity and other actions which degrade the quality of the fines so that they can be used only in second line cheeses.
To solve that problem, an in-line system for recovering fines was developed. In that system, the whey draining out of the drain table is pumped across, rather than through, a series of planar mesh screens. This is done under pressure in a liquid filled container from which there is one outlet for the purified whey and another outlet from which a thicker slurry of whey and fines is pumped back to the drain table. This system was unsatisfactory because the screens tended to clog and because it was unable to meet the sanitation requirements of the Food and Drug Administration and the United States Department of Agriculture.